The present invention relates generally to crucibles for melting and pouring metals and, more particularly, to a crucible for delivering molten metal in a steady stream without clogging the exit orifice thereof.
In order to facilitate measurement, handling, pouring, and rapid and uniform melting, metal that is to be melted for molding purposes such as for jewelry, dental crowns, sheeting, etc., is generally formed into uniform grains or granules.
In the process of graining, or generating small particles of a metal from the liquid metal, the metal is commonly melted in a crucible having an exit orifice located in the bottom portion thereof. Solid metal is introduced into the crucible through its open upper portion, and melted by heating the crucible. To obtain uniform grain size of the particles exiting the crucible orifice, the temperature of the metal and the pressure head of the liquid above the orifice must both be substantially maintained at chosen values. Crucibles currently used for this purpose simply have holes in the lower portion thereof which essentially permit liquid flow as soon as liquid metal is formed in the crucible above the orifices.
One manner in which uniform grain size may be achieved is described in U.S. Pat. No. 4,986,941 for "Shotting Apparatus and Process," which issued on Jan. 22, 1991 to Loren E. Hendrix and Alan B. Mistrater. The inventors disclose a shotting apparatus which comprises a chamber for containing a molten material and a plate with a plurality of orifices through which the molten material can pass to form droplets. A head of molten metal is achieved by regulating the flow of molten material to the chamber through an entrance in its upper portion. It appears that the apparatus is heated by the molten metal introduced thereto.
Additionally, since the solid metal added to a crucible is often impure, the impurities generally having lower density than the metal itself, it is necessary to prevent materials in the proximity of the surface of the molten metal from exiting through the orifice, both to reduce the tendency of the orifice from becoming clogged, and to prevent the formation of grains which are substantially different in composition from the desired metal. It is assumed that Hendrix et al., supra, have solved this problem with some sort of metal purification before the liquid metal is introduced into the apparatus.
Accordingly, it is an object of the present invention to provide an apparatus for generating uniform droplets of molten metal for graining purposes.
Another object of the invention is to provide an apparatus for generating uniform droplets of molten metal which have uniform composition for graining purposes.
Yet another object of the invention is to provide an apparatus for efficiently melting and pouring metals.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.